Beam transforming element, illumination optical apparatus, exposure apparatus, and exposure method with two optical elements having different thicknesses

ABSTRACT

A beam transforming element for forming a predetermined light intensity distribution on a predetermined surface on the basis of an incident beam includes a first basic element made of an optical material with optical activity, for forming a first region distribution of the predetermined light intensity distribution on the basis of the incident beam; and a second basic element made of an optical material with optical activity, for forming a second region distribution of the predetermined light intensity distribution on the basis of the incident beam, wherein the first basic element and the second basic element have their respective thicknesses different from each other along a direction of transmission of light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 13/137,002 filed on Jul.14, 2011, which is a continuation of application Ser. No. 12/461,852filed on Aug. 26, 2009 (abandoned), which is a continuation ofapplication Ser. No. 11/319,057 filed on Dec. 28, 2005 (abandoned),which is a continuation-in-part of Application No. PCT/JP2004/016247filed on Nov. 2, 2004, which claims the benefit of Japanese ApplicationNo. 2003-390674 filed on Nov. 20, 2003. The disclosures of the priorapplications are incorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a beam transforming element,illumination optical apparatus, exposure apparatus, and exposure methodand, more particularly, to an illumination optical apparatus suitablyapplicable to exposure apparatus used in production of microdevices suchas semiconductor elements, image pickup elements, liquid crystal displayelements, and thin-film magnetic heads by lithography.

2. Related Background Art

In the typical exposure apparatus of this type, a beam emitted from alight source travels through a fly's eye lens as an optical integratorto form a secondary light source as a substantial surface illuminantconsisting of a number of light sources. Beams from the secondary lightsource (generally, an illumination pupil distribution formed on or nearan illumination pupil of the illumination optical apparatus) are limitedthrough an aperture stop disposed near the rear focal plane of the fly'seye lens and then enter a condenser lens.

The beams condensed by the condenser lens superposedly illuminate a maskon which a predetermined pattern is formed. The light passing throughthe pattern of the mask is focused on a wafer through a projectionoptical system. In this manner, the mask pattern is projected forexposure (or transcribed) onto the wafer. The pattern formed on the maskis a highly integrated pattern, and, in order to accurately transcribethis microscopic pattern onto the wafer, it is indispensable to obtain auniform illuminance distribution on the wafer.

For example, Japanese Patent No. 3246615 owned by the same Applicant ofthe present application discloses the following technology for realizingthe illumination condition suitable for faithful transcription of themicroscopic pattern in arbitrary directions: the secondary light sourceis formed in an annular shape on the rear focal plane of the fly's eyelens and the beams passing the secondary light source of the annularshape are set to be in a linearly polarized state with a direction ofpolarization along the circumferential direction thereof (hereinafterreferred to as a “azimuthal polarization state”).

SUMMARY OF THE INVENTION

An object of the present invention is to form an illumination pupildistribution of an annular shape in a azimuthal polarization state whilewell suppressing the loss of light quantity. Another object of thepresent invention is to transcribe a microscopic pattern in an arbitrarydirection under an appropriate illumination condition faithfully andwith high throughput, by forming an illumination pupil distribution ofan annular shape in a azimuthal polarization state while wellsuppressing the loss of light quantity.

In order to achieve the above objects, a first aspect of the presentembodiment is to provide a beam transforming element for forming apredetermined light intensity distribution on a predetermined surface onthe basis of an incident beam, comprising:

a first basic element made of an optical material with optical activity,for forming a first region distribution of the predetermined lightintensity distribution on the basis of the incident beam; and

a second basic element made of an optical material with opticalactivity, for forming a second region distribution of the predeterminedlight intensity distribution on the basis of the incident beam,

wherein the first basic element and the second basic element have theirrespective thicknesses different from each other along a direction oftransmission of light.

A second aspect of the present embodiment is to provide a beamtransforming element for, based on an incident beam, forming apredetermined light intensity distribution of a shape different from asectional shape of the incident beam, on a predetermined surface,comprising:

a diffracting surface or a refracting surface for forming thepredetermined light intensity distribution on the predetermined surface,

wherein the predetermined light intensity distribution is a distributionin at least a part of a predetermined annular region, which is apredetermined annular region centered around a predetermined point onthe predetermined surface, and

wherein a beam from the beam transforming element passing through thepredetermined annular region has a polarization state in which aprincipal component is linearly polarized light having a direction ofpolarization along a circumferential direction (azymuthally direction)of the predetermined annular region.

A third aspect of the present invention is to provide an illuminationoptical apparatus for illuminating a surface to be illuminated, based ona beam from a light source, comprising:

the beam transforming element of the first aspect or the second aspectfor transforming the beam from the light source in order to form anillumination pupil distribution on or near an illumination pupil of theillumination optical apparatus.

A fourth aspect of the present embodiment is to provide an exposureapparatus comprising the illumination optical apparatus of the thirdaspect for illuminating a pattern,

the exposure apparatus being arranged to project the pattern onto aphotosensitive substrate.

A fifth aspect of the present embodiment is to provide an exposuremethod comprising: an illumination step of illuminating a pattern by useof the illumination optical apparatus of the third aspect; and anexposure step of projecting the pattern onto a photosensitive substrate.

The illumination optical apparatus of the present embodiment, differentfrom the conventional technology giving rise to the large loss of lightquantity at the aperture stop, is able to form the illumination pupildistribution of the annular shape in the azimuthal polarization state,with no substantial loss of light quantity, by diffraction and opticalrotating action of the diffractive optical element as the beamtransforming element. Namely, the illumination optical apparatus of thepresent invention is able to form the illumination pupil distribution ofthe annular shape in the azimuthal polarization state while wellsuppressing the loss of light quantity.

Since the exposure apparatus and exposure method using the illuminationoptical apparatus of the present embodiment are arranged to use theillumination optical apparatus capable of forming the illumination pupildistribution of the annular shape in the azimuthal polarization statewhile well suppressing the loss of light quantity, they are able totranscribe a microscopic pattern in an arbitrary direction under anappropriate illumination condition faithfully and with high throughputand, in turn, to produce good devices with high throughput.

The present invention will be more fully understood from the detaileddescription given hereinbelow and the accompanying drawings, which aregiven by way of illustration only and are not to be considered aslimiting the embodiment.

Further scope of applicability of the embodiment will become apparentfrom the detailed description given hereinafter. However, it should beunderstood that the detailed description and specific examples, whileindicating preferred embodiments of the invention, are given by way ofillustration only, since various changes and modifications within thespirit and scope of the invention will be apparent to those skilled inthe art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration schematically showing a configuration of anexposure apparatus with an illumination optical apparatus according toan embodiment of the present invention.

FIG. 2 is an illustration showing a secondary light source of an annularshape formed in annular illumination.

FIG. 3 is an illustration schematically showing a configuration of aconical axicon system disposed in an optical path between a front lensunit and a rear lens unit of an afocal lens in FIG. 1.

FIG. 4 is an illustration to illustrate the action of the conical axiconsystem on the secondary light source of the annular shape.

FIG. 5 is an illustration to illustrate the action of a zoom lens on thesecondary light source of the annular shape.

FIG. 6 is an illustration schematically showing a first cylindrical lenspair and a second cylindrical lens pair disposed in an optical pathbetween the front lens unit and the rear lens unit of the afocal lens inFIG. 1.

FIG. 7 is a first drawing to illustrate the action of the firstcylindrical lens pair and the second cylindrical lens pair on thesecondary light source of the annular shape.

FIG. 8 is a second drawing to illustrate the action of the firstcylindrical lens pair and the second cylindrical lens pair on thesecondary light source of the annular shape.

FIG. 9 is a third drawing to illustrate the action of the firstcylindrical lens pair and the second cylindrical lens pair on thesecondary light source of the annular shape.

FIG. 10 is a perspective view schematically showing an internalconfiguration of a polarization monitor in FIG. 1.

FIG. 11 is an illustration schematically showing a configuration of adiffractive optical element for azimuthally polarized annularillumination according to an embodiment of the present invention.

FIG. 12 is an illustration schematically showing a secondary lightsource of an annular shape set in the azimuthal polarization state.

FIG. 13 is an illustration to illustrate the action of a first basicelement.

FIG. 14 is an illustration to illustrate the action of a second basicelement.

FIG. 15 is an illustration to illustrate the action of a third basicelement.

FIG. 16 is an illustration to illustrate the action of a fourth basicelement.

FIG. 17 is an illustration to illustrate the optical activity ofcrystalline quartz.

FIGS. 18A and 18B are illustrations showing octapole secondary lightsources in the azimuthal polarization state consisting of eight arcregions spaced from each other along the circumferential direction and aquadrupole secondary light source in the azimuthal polarization stateconsisting of four arc regions spaced from each other along thecircumferential direction.

FIG. 19 is an illustration showing a secondary light source of anannular shape in the azimuthal polarization state consisting of eightarc regions overlapping with each other along the circumferentialdirection.

FIGS. 20A and 20B are illustrations showing hexapole secondary lightsources in the azimuthal polarization state consisting of six arcregions spaced from each other along the circumferential direction and asecondary light source in the azimuthal polarization state having aplurality of regions spaced from each other along the circumferentialdirection and a region on the optical axis.

FIG. 21 is an illustration showing an example in which an entrance-sidesurface of a diffractive optical element for azimuthally polarizedannular illumination is planar.

FIG. 22 is a flowchart of a procedure of obtaining semiconductor devicesas microdevices.

FIG. 23 is a flowchart of a procedure of obtaining a liquid crystaldisplay element as a microdevice.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described based on theaccompanying drawings.

FIG. 1 is an illustration schematically showing a configuration of anexposure apparatus with an illumination optical apparatus according toan embodiment of the present invention. In FIG. 1, the Z-axis is definedalong a direction of a normal to a wafer W being a photosensitivesubstrate, the Y-axis along a direction parallel to the plane of FIG. 1in the plane of the wafer W, and the X-axis along a direction of anormal to the plane of FIG. 1 in the plane of wafer W. The exposureapparatus of the present embodiment is provided with a light source 1for supplying exposure light (illumination light).

The light source 1 can be, for example, a KrF excimer laser light sourcefor supplying light with the wavelength of 248 nm, an ArF excimer laserlight source for supplying light with the wavelength of 193 nm, or thelike. A nearly parallel beam emitted along the Z-direction from thelight source 1 has a cross section of a rectangular shape elongatedalong the X-direction, and is incident to a beam expander 2 consistingof a pair of lenses 2 a and 2 b. The lenses 2 a and 2 b have a negativerefracting power and a positive refracting power, respectively, in theplane of FIG. 1 (or in the YZ plane). Therefore, the beam incident tothe beam expander 2 is enlarged in the plane of FIG. 1 and shaped into abeam having a cross section of a predetermined rectangular shape.

The nearly parallel beam passing through the beam expander 2 as a beamshaping optical system is deflected into the Y-direction by a bendingmirror 3, and then travels through a quarter wave plate 4 a, a half waveplate 4 b, a depolarizer (depolarizing element) 4 c, and a diffractiveoptical element 5 for annular illumination to enter an afocal lens 6.Here the quarter wave plate 4 a, half wave plate 4 b, and depolarizer 4c constitute a polarization state converter 4, as described later. Theafocal lens 6 is an afocal system (afocal optic) set so that the frontfocal position thereof approximately coincides with the position of thediffractive optical element 5 and so that the rear focal positionthereof approximately coincides with the position of a predeterminedplane 7 indicated by a dashed line in the drawing.

In general, a diffractive optical element is constructed by forminglevel differences with the pitch of approximately the wavelength ofexposure light (illumination light) in a substrate and has the action ofdiffracting an incident beam at desired angles. Specifically, thediffractive optical element 5 for annular illumination has the followingfunction: when a parallel beam having a rectangular cross section isincident thereto, it forms a light intensity distribution of an annularshape in its far field (or Fraunhofer diffraction region). Therefore,the nearly parallel beam incident to the diffractive optical element 5as a beam transforming element forms a light intensity distribution ofan annular shape on the pupil plane of the afocal lens 6 and thenemerges as a nearly parallel beam from the afocal lens 6.

In an optical path between front lens unit 6 a and rear lens unit 6 b ofthe afocal lens 6 there are a conical axicon system 8, a firstcylindrical lens pair 9, and a second cylindrical lens pair 10 arrangedin order from the light source side on or near the pupil plane of theafocal lens, and the detailed configuration and action thereof will bedescribed later. For easier description, the fundamental configurationand action will be described below, in disregard of the action of theconical axicon system 8, first cylindrical lens pair 9, and secondcylindrical lens pair 10.

The beam through the afocal lens 6 travels through a zoom lens 11 forvariation of σ-value and then enters a micro fly's eye lens (or fly'seye lens) 12 as an optical integrator. The micro fly's eye lens 12 is anoptical element consisting of a number of micro lenses with a positiverefracting power arranged lengthwise and breadthwise and densely. Ingeneral, a micro fly's eye lens is constructed, for example, by forminga micro lens group by etching of a plane-parallel plate.

Here each micro lens forming the micro fly's eye lens is much smallerthan each lens element forming a fly's eye lens. The micro fly's eyelens is different from the fly's eye lens consisting of lens elementsspaced from each other, in that a number of micro lenses (microrefracting surfaces) are integrally formed without being separated fromeach other. In the sense that lens elements with a positive refractingpower are arranged lengthwise and breadthwise, however, the micro fly'seye lens is a wavefront splitting optical integrator of the same type asthe fly's eye lens. Detailed explanation concerning the micro fly's eyelens capable of being used in the present invention is disclosed, forexample, in U.S. Pat. No. 6,913,373(B2) which is incorporated herein byreference in its entirety.

The position of the predetermined plane 7 is arranged near the frontfocal position of the zoom lens 11, and the entrance surface of themicro fly's eye lens 12 is arranged near the rear focal position of thezoom lens 11. In other words, the zoom lens 11 arranges thepredetermined plane 7 and the entrance surface of the micro fly's eyelens 12 substantially in the relation of Fourier transform andeventually arranges the pupil plane of the afocal lens 6 and theentrance surface of the micro fly's eye lens 12 approximately opticallyconjugate with each other.

Accordingly, for example, an illumination field of an annular shapecentered around the optical axis AX is formed on the entrance surface ofthe micro fly's eye lens 12, as on the pupil plane of the afocal lens 6.The entire shape of this annular illumination field similarly variesdepending upon the focal length of the zoom lens 11. Each micro lensforming the micro fly's eye lens 12 has a rectangular cross sectionsimilar to a shape of an illumination field to be formed on a mask M(eventually, a shape of an exposure region to be formed on a wafer W).

The beam incident to the micro fly's eye lens 12 is two-dimensionallysplit by a number of micro lenses to form on its rear focal plane(eventually on the illumination pupil) a secondary light source havingmuch the same light intensity distribution as the illumination fieldformed by the incident beam, i.e., a secondary light source consistingof a substantial surface illuminant of an annular shape centered aroundthe optical axis AX, as shown in FIG. 2. Beams from the secondary lightsource formed on the rear focal plane of the micro fly's eye lens 12 (ingeneral, an illumination pupil distribution formed on or near the pupilplane of the illumination optical apparatus) travel through beamsplitter 13 a and condenser optical system 14 to superposedly illuminatea mask blind 15.

In this manner, an illumination field of a rectangular shape accordingto the shape and focal length of each micro lens forming the micro fly'seye lens 12 is formed on the mask blind 15 as an illumination fieldstop. The internal configuration and action of polarization monitor 13incorporating a beam splitter 13 a will be described later. Beam througha rectangular aperture (light transmitting portion) of the mask blind 15are subject to light condensing action of imaging optical system 16 andthereafter superposedly illuminate the mask M on which a predeterminedpattern is formed.

Namely, the imaging optical system 16 forms an image of the rectangularaperture of the mask blind 15 on the mask M. A beam passing through thepattern of mask M travels through a projection optical system PL to forman image of the mask pattern on the wafer W being a photosensitivesubstrate. In this manner, the pattern of the mask M is sequentiallyprinted in each exposure area on the wafer W through full-wafer exposureor scan exposure with two-dimensional drive control of the wafer Win theplane (XY plane) perpendicular to the optical axis AX of the projectionoptical system PL.

In the polarization state converter 4, the quarter wave plate 4 a isarranged so that its crystallographic axis is rotatable around theoptical axis AX, and it transforms incident light of ellipticalpolarization into light of linear polarization. The half wave plate 4 bis arranged so that its crystallographic axis is rotatable around theoptical axis AX, and it changes the plane of polarization of linearlypolarized light incident thereto. The depolarizer 4 c is composed of awedge-shaped crystalline quartz prism (not shown) and a wedge-shapedfused sillica prism (not shown) having complementary shapes. Thecrystalline quartz prism and the fussed sillica prism are constructed asan integral prism assembly so as to be set into and away from theillumination optical path.

Where the light source 1 is the KrF excimer laser light source or theArF excimer laser light source, light emitted from these light sourcestypically has the degree of polarization of 95% or more and light ofalmost linear polarization is incident to the quarter wave plate 4 a.However, if a right-angle prism as a back-surface reflector isinterposed in the optical path between the light source 1 and thepolarization state converter 4, the linearly polarized light will bechanged into elliptically polarized light by virtue of total reflectionin the right-angle prism unless the plane of polarization of theincident, linearly polarized light agrees with the P-polarization planeor S-polarization plane.

In the case of the polarization state converter 4, for example, even iflight of elliptical polarization is incident thereto because of thetotal reflection in the right-angle prism, light of linear polarizationtransformed by the action of the quarter wave plate 4 a will be incidentto the half wave plate 4 b. Where the crystallographic axis of the halfwave plate 4 b is set at an angle of 0° or 90° relative to the plane ofpolarization of the incident, linearly polarized light, the light oflinear polarization incident to the half wave plate 4 b will pass as itis, without change in the plane of polarization.

Where the crystallographic axis of the half wave plate 4 b is set at anangle of 45° relative to the plane of polarization of the incident,linearly polarized light, the light of linear polarization incident tothe half wave plate 4 b will be transformed into light of linearpolarization with change of polarization plane of 90°. Furthermore,where the crystallographic axis of the crystalline quartz prism in thedepolarizer 4 c is set at an angle of 45° relative to the polarizationplane of the incident, linearly polarized light, the light of linearpolarization incident to the crystalline quartz prism will betransformed (or depolarized) into light in an unpolarized state.

The polarization state converter 4 is arranged as follows: when thedepolarizer 4 c is positioned in the illumination optical path, thecrystallographic axis of the crystalline quartz prism makes the angle of45° relative to the polarization plane of the incident, linearlypolarized light. Incidentally, where the crystallographic axis of thecrystalline quartz prism is set at the angle of 0° or 90° relative tothe polarization plane of the incident, linearly polarized light, thelight of linear polarization incident to the crystalline quartz prismwill pass as it is, without change of the polarization plane. Where thecrystallographic axis of the half wave plate 4 b is set at an angle of22.5° relative to the polarization plane of incident, linearly polarizedlight, the light of linear polarization incident to the half wave plate4 b will be transformed into light in an unpolarized state including alinear polarization component directly passing without change of thepolarization plane and a linear polarization component with thepolarization plane rotated by 90°.

The polarization state converter 4 is arranged so that light of linearpolarization is incident to the half wave plate 4 b, as described above,and, for easier description hereinafter, it is assumed that light oflinear polarization having the direction of polarization (direction ofthe electric field) along the Z-axis in FIG. 1 (hereinafter referred toas “Z-directionally polarized light”) is incident to the half wave plate4 b. When the depolarizer 4 c is positioned in the illumination opticalpath and when the crystallographic axis of the half wave plate 4 b isset at the angle of 0° or 90° relative to the polarization plane(direction of polarization) of the Z-directionally polarized lightincident thereto, the light of Z-directional polarization incident tothe half wave plate 4 b passes as kept as Z-directionally polarizedlight without change of the polarization plane and enters thecrystalline quartz prism in the depolarizer 4 c. Since thecrystallographic axis of the crystalline quartz prism is set at theangle of 45° relative to the polarization plane of the Z-directionallypolarized light incident thereto, the light of Z-directionalpolarization incident to the crystalline quartz prism is transformedinto light in an unpolarized state.

The light depolarized through the crystalline quartz prism travelsthrough the quartz prism as a compensator for compensating the travelingdirection of the light and is incident into the diffractive opticalelement 5 while being in the depolarized state. On the other hand, ifthe crystallographic axis of the half wave plate 4 b is set at the angleof 45° relative to the polarization plane of the Z-directionallypolarized light incident thereto, the light of Z-directionalpolarization incident to the half wave plate 4 b will be rotated in thepolarization plane by 90° and transformed into light of linearpolarization having the polarization direction (direction of theelectric field) along the X-direction in FIG. 1 (hereinafter referred toas “X-directionally polarized light”) and the X-directionally polarizedlight will be incident to the crystalline quartz prism in thedepolarizer 4 c. Since the crystallographic axis of the crystallinequartz prism is set at the angle of 45° relative to the polarizationplane of the incident, X-directionally polarized light as well, thelight of X-directional polarization incident to the crystalline quartzprism is transformed into light in the depolarized state, and the lighttravels through the quartz prism to be incident in the depolarized stateinto the diffractive optical element 5.

In contrast, when the depolarizer 4 c is set away from the illuminationoptical path, if the crystallographic axis of the half wave plate 4 b isset at the angle of 0° or 90° relative to the polarization plane of theZ-directionally polarized light incident thereto, the light ofZ-directional polarization incident to the half wave plate 4 b will passas kept as Z-directionally polarized light without change of thepolarization plane, and will be incident in the Z-directionallypolarized state into the diffractive optical element 5. If thecrystallographic axis of the half wave plate 4 b is set at the angle of45° relative to the polarization plane of the Z-directionally polarizedlight incident thereto on the other hand, the light of Z-directionalpolarization incident to the half wave plate 4 b will be transformedinto light of X-directional polarization with the polarization planerotated by 90°, and will be incident in the X-directionally polarizedstate into the diffractive optical element 5.

In the polarization state converter 4, as described above, the light inthe depolarized state can be made incident to the diffractive opticalelement 5 when the depolarizer 4 c is set and positioned in theillumination optical path. When the depolarizer 4 c is set away from theillumination optical path and when the crystallographic axis of the halfwave plate 4 b is set at the angle of 0° or 90° relative to thepolarization plane of the Z-directionally polarized light incidentthereto, the light in the Z-directionally polarized state can be madeincident to the diffractive optical element 5. Furthermore, when thedepolarizer 4 c is set away from the illumination optical path and whenthe crystallographic axis of the half wave plate 4 b is set at the angleof 45° relative to the polarization plane of the Z-directionallypolarized light incident thereto, the light in the X-directionallypolarized state can be made incident to the diffractive optical element5.

In other words, the polarization state converter 4 is able to switch thepolarization state of the incident light into the diffractive opticalelement 5 (a state of polarization of light to illuminate the mask M andwafer W in use of an ordinary diffractive optical element except for thediffractive optical element for azimuthally polarized annularillumination according to the present invention as will be describedlater) between the linearly polarized state and the unpolarized statethrough the action of the polarization state converter consisting of thequarter wave plate 4 a, half wave plate 4 b, and depolarizer 4 c, and,in the case of the linearly polarized state, it is able to switchbetween mutually orthogonal polarization states (between theZ-directional polarization and the X-directional polarization).

FIG. 3 is an illustration schematically showing the configuration of theconical axicon system disposed in the optical path between the frontlens unit and the rear lens unit of the afocal lens in FIG. 1. Theconical axicon system 8 is composed of a first prism member 8 a whoseplane is kept toward the light source and whose refracting surface of aconcave conical shape is kept toward the mask, and a second prism member8 b whose plane is kept toward the mask and whose refracting surface ofa convex conical shape is kept toward the light source, in order fromthe light source side.

The refracting surface of the concave conical shape of the first prismmember 8 a and the refracting surface of the convex conical shape of thesecond prism member 8 b are formed in a complementary manner so as to beable to be brought into contact with each other. At least one of thefirst prism member 8 a and the second prism member 8 b is arrangedmovable along the optical axis AX, so that the spacing can be variedbetween the refracting surface of the concave conical shape of the firstprism member 8 a and the refracting surface of the convex conical shapeof the second prism member 8 b.

In a state in which the refracting surface of the concave conical shapeof the first prism member 8 a and the refracting surface of the convexconical shape of the second prism member 8 b are in contact with eachother, the conical axicon system 8 functions as a plane-parallel plateand has no effect on the secondary light source of the annular shapeformed. However, when the refracting surface of the concave conicalshape of the first prism member 8 a and the refracting surface of theconvex conical shape of the second prism member 8 b are spaced from eachother, the conical axicon system 8 functions a so-called beam expander.Therefore, the angle of the incident beam to the predetermined plane 7varies according to change in the spacing of the conical axicon system8.

FIG. 4 is an illustration to illustrate the action of the conical axiconsystem on the secondary light source of the annular shape. Withreference to FIG. 4, the secondary light source 30 a of the minimumannular shape formed in a state where the spacing of the conical axiconsystem 8 is zero and where the focal length of the zoom lens 11 is setat the minimum (this state will be referred to hereinafter as a“standard state”) is changed into secondary light source 30 b of anannular shape with the outside diameter and inside diameter bothenlarged and without change in the width (half of the difference betweenthe inside diameter and the outside diameter: indicated by arrows in thedrawing) when the spacing of the conical axicon system 8 is increasedfrom zero to a predetermined value. In other words, an annular ratio(inside diameter/outside diameter) and size (outside diameter) both varythrough the action of the conical axicon system 8, without change in thewidth of the secondary light source of the annular shape.

FIG. 5 is an illustration to illustrate the action of the zoom lens onthe secondary light source of the annular shape. With reference to FIG.5, the secondary light source 30 a of the annular shape formed in thestandard state is changed into secondary light source 30 c of an annularshape whose entire shape is similarly enlarged by increasing the focallength of the zoom lens 11 from the minimum to a predetermined value. Inother words, the width and size (outside diameter) both vary through theaction of zoom lens 11, without change in the annular ratio of thesecondary light source of the annular shape.

FIG. 6 is an illustration schematically showing the configuration of thefirst cylindrical lens pair and the second cylindrical lens pairdisposed in the optical path between the front lens unit and the rearlens unit of the afocal lens in FIG. 1. In FIG. 6, the first cylindricallens pair 9 and the second cylindrical lens pair 10 are arranged inorder from the light source side. The first cylindrical lens pair 9 iscomposed, for example, of a first cylindrical negative lens 9 a with anegative refracting power in the YZ plane and with no refracting powerin the XY plane, and a first cylindrical positive lens 9 b with apositive refracting power in the YZ plane and with no refracting powerin the XY plane, which are arranged in order from the light source side.

On the other hand, the second cylindrical lens pair 10 is composed, forexample, of a second cylindrical negative lens 10 a with a negativerefracting power in the XY plane and with no refracting power in the YZplane, and a second cylindrical positive lens 10 b with a positiverefracting power in the XY plane and with no refracting power in the YZplane, which are arranged in order from the light source side. The firstcylindrical negative lens 9 a and the first cylindrical positive lens 9b are arranged so as to integrally rotate around the optical axis AX.Similarly, the second cylindrical negative lens 10 a and the secondcylindrical positive lens 10 b are arranged so as to integrally rotatearound the optical axis AX.

In the state shown in FIG. 6, the first cylindrical lens pair 9functions as a beam expander having a power in the Z-direction, and thesecond cylindrical lens pair 10 as a beam expander having a power in theX-direction. The power of the first cylindrical lens pair 9 and thepower of the second cylindrical lens pair 10 are set to be equal to eachother.

FIGS. 7 to 9 are illustrations to illustrate the action of the firstcylindrical lens pair and the second cylindrical lens pair on thesecondary light source of the annular shape. FIG. 7 shows such a settingthat the direction of the power of the first cylindrical lens pair 9makes the angle of +45° around the optical axis AX relative to theZ-axis and that the direction of the power of the second cylindricallens pair 10 makes the angle of −45° around the optical axis AX relativeto the Z-axis.

Therefore, the direction of the power of the first cylindrical lens pair9 is perpendicular to the direction of the power of the secondcylindrical lens pair 10, and the composite system of the firstcylindrical lens pair 9 and the second cylindrical lens pair 10 has theZ-directional power and the X-directional power identical to each other.As a result, in a perfect circle state shown in FIG. 7, a beam passingthrough the composite system of the first cylindrical lens pair 9 andthe second cylindrical lens pair 10 is subject to enlargement at thesame power in the Z-direction and in the X-direction to form thesecondary light source of a perfect-circle annular shape on theillumination pupil.

In contrast to it, FIG. 8 shows such a setting that the direction of thepower of the first cylindrical lens pair 9 makes, for example, the angleof +80° around the optical axis AX relative to the Z-axis and that thedirection of the power of the second cylindrical lens pair 10 makes, forexample, the angle of −80° around the optical axis AX relative to theZ-axis. Therefore, the power in the X-direction is greater than thepower in the Z-direction in the composite system of the firstcylindrical lens pair 9 and the second cylindrical lens pair 10. As aresult, in a horizontally elliptic state shown in FIG. 8, the beampassing through the composite system of the first cylindrical lens pair9 and the second cylindrical lens pair 10 is subject to enlargement atthe power greater in the X-direction than in the Z-direction, wherebythe secondary light source of a horizontally long annular shapeelongated in the X-direction is formed on the illumination pupil.

On the other hand, FIG. 9 shows such a setting that the direction of thepower of the first cylindrical lens pair 9 makes, for example, the angleof +10° around the optical axis AX relative to the Z-axis and that thedirection of the power of the second cylindrical lens pair 10 makes, forexample, the angle of −10° around the optical axis AX relative to theZ-axis. Therefore, the power in the Z-direction is greater than thepower in the X-direction in the composite system of the firstcylindrical lens pair 9 and the second cylindrical lens pair 10. As aresult, in a vertically elliptical state shown in FIG. 9, the beampassing through the composite system of the first cylindrical lens pair9 and the second cylindrical lens pair 10 is subject to enlargement atthe power greater in the Z-direction than in the X-direction, wherebythe secondary light source of a vertically long annular shape elongatedin the Z-direction is formed on the illumination pupil.

Furthermore, by setting the first cylindrical lens pair 9 and the secondcylindrical lens pair 10 in an arbitrary state between the perfectcircle state shown in FIG. 7 and the horizontally elliptical state shownin FIG. 8, the secondary light source can be formed in a horizontallylong annular shape according to any one of various aspect ratios. Bysetting the first cylindrical lens pair 9 and the second cylindricallens pair 10 in an arbitrary state between the perfect circle stateshown in FIG. 7 and the vertically elliptical state shown in FIG. 9, thesecondary light source can be formed in a vertically long annular shapeaccording to any one of various aspect ratios.

FIG. 10 is a perspective view schematically showing the internalconfiguration of the polarization monitor shown in FIG. 1. Withreference to FIG. 10, the polarization monitor 10 is provided with afirst beam splitter 13 a disposed in the optical path between the microfly's eye lens 12 and the condenser optical system 14. The first beamsplitter 13 a has, for example, the form of a non-coated plane-parallelplate made of quartz glass (i.e., raw glass), and has a function oftaking reflected light in a polarization state different from apolarization state of incident light, out of the optical path.

The light taken out of the optical path by the first beam splitter 13 ais incident to a second beam splitter 13 b. The second beam splitter 13b has, for example, the form of a non-coated plane-parallel plate madeof quartz glass as the first beam splitter 13 a does, and has a functionof generating reflected light in a polarization state different from thepolarization state of incident light. The polarization monitor is so setthat the P-polarized light for the first beam splitter 13 a becomes theS-polarized light for the second beam splitter 13 b and that theS-polarized light for the first beam splitter 13 a becomes theP-polarized light for the second beam splitter 13 b.

Light transmitted by the second beam splitter 13 b is detected by firstlight intensity detector 13 c, while light reflected by the second beamsplitter 13 b is detected by second light intensity detector 13 d.Outputs from the first light intensity detector 13 c and from the secondlight intensity detector 13 d are supplied each to a controller (notshown). The controller drives the quarter wave plate 4 a, half waveplate 4 b, and depolarizer 4 c constituting the polarization stateconverter 4, according to need.

As described above, the reflectance for the P-polarized light and thereflectance for the S-polarized light are substantially different in thefirst beam splitter 13 a and in the second beam splitter 13 b. In thepolarization monitor 13, therefore, the reflected light from the firstbeam splitter 13 a includes the S-polarization component (i.e., theS-polarization component for the first beam splitter 13 a andP-polarization component for the second beam splitter 13 b), forexample, which is approximately 10% of the incident light to the firstbeam splitter 13 a, and the P-polarization component (i.e., theP-polarization component for the first beam splitter 13 a andS-polarization component for the second beam splitter 13 b), forexample, which is approximately 1% of the incident light to the firstbeam splitter 13 a.

The reflected light from the second beam splitter 13 b includes theP-polarization component (i.e., the P-polarization component for thefirst beam splitter 13 a and S-polarization component for the secondbeam splitter 13 b), for example, which is approximately 10%×1%=0.1% ofthe incident light to the first beam splitter 13 a, and theS-polarization component (i.e., the S-polarization component for thefirst beam splitter 13 a and P-polarization component for the secondbeam splitter 13 b), for example, which is approximately 1%×10%=0.1% ofthe incident light to the first beam splitter 13 a.

In the polarization monitor 13, as described above, the first beamsplitter 13 a has the function of extracting the reflected light in thepolarization state different from the polarization state of the incidentlight out of the optical path in accordance with its reflectioncharacteristic. As a result, though there is slight influence ofvariation of polarization due to the polarization characteristic of thesecond beam splitter 13 b, it is feasible to detect the polarizationstate (degree of polarization) of the incident light to the first beamsplitter 13 a and, therefore, the polarization state of the illuminationlight to the mask M, based on the output from the first light intensitydetector 13 c (information about the intensity of transmitted light fromthe second beam splitter 13 b, i.e., information about the intensity oflight virtually in the same polarization state as that of the reflectedlight from the first beam splitter 13 a).

The polarization monitor 13 is so set that the P-polarized light for thefirst beam splitter 13 a becomes the S-polarized light for the secondbeam splitter 13 b and that the S-polarized light for the first beamsplitter 13 a becomes the P-polarized light for the second beam splitter13 b. As a result, it is feasible to detect the light quantity(intensity) of the incident light to the first beam splitter 13 a and,therefore, the light quantity of the illumination light to the mask M,with no substantial effect of change in the polarization state of theincident light to the first beam splitter 13 a, based on the output fromthe second light intensity detector 13 d (information about theintensity of light successively reflected by the first beam splitter 13a and the second beam splitter 13 b).

In this manner, it is feasible to detect the polarization state of theincident light to the first beam splitter 13 a and, therefore, todetermine whether the illumination light to the mask M is in the desiredunpolarized state or linearly polarized state, using the polarizationmonitor 13. When the controller determines that the illumination lightto the mask M (eventually, to the wafer W) is not in the desiredunpolarized state or linearly polarized state, based on the detectionresult of the polarization monitor 13, it drives and adjusts the quarterwave plate 4 a, half wave plate 4 b, and depolarizer 4 c constitutingthe polarization state converter 4 so that the state of the illuminationlight to the mask M can be adjusted into the desired unpolarized stateor linearly polarized state.

Quadrupole illumination can be implemented by setting a diffractiveoptical element for quadrupole illumination (not shown) in theillumination optical path, instead of the diffractive optical element 5for annular illumination. The diffractive optical element for quadrupoleillumination has such a function that when a parallel beam having arectangular cross section is incident thereto, it forms a lightintensity distribution of a quadrupole shape in the far field thereof.Therefore, the beam passing through the diffractive optical element forquadrupole illumination forms an illumination field of a quadrupoleshape consisting of four circular illumination fields centered aroundthe optical axis AX, for example, on the entrance surface of the microfly's eye lens 12. As a result, the secondary light source of the samequadrupole shape as the illumination field formed on the entrancesurface is also formed on the rear focal plane of the micro fly's eyelens 12.

In addition, ordinary circular illumination can be implemented bysetting a diffractive optical element for circular illumination (notshown) in the illumination optical path, instead of the diffractiveoptical element 5 for annular illumination. The diffractive opticalelement for circular illumination has such a function that when aparallel beam having a rectangular cross section is incident thereto, itforms a light intensity distribution of a circular shape in the farfield. Therefore, a beam passing through the diffraction optical elementfor circular illumination forms a circular illumination field centeredaround the optical axis AX, for example, on the entrance plane of themicro fly's eye lens 12. As a result, the secondary light source of thesame circular shape as the illumination field formed on the entrancesurface is also formed on the rear focal plane of the micro fly's eyelens 12.

Furthermore, a variety of multipole illuminations (dipole illumination,octapole illumination, etc.) can be implemented by setting otherdiffractive optical elements for multipole illuminations (not shown),instead of the diffractive optical element 5 for annular illumination.Likewise, modified illuminations in various forms can be implemented bysetting diffractive optical elements with appropriate characteristics(not shown) in the illumination optical path, instead of the diffractiveoptical element 5 for annular illumination.

In the present embodiment, a diffractive optical element 50 forso-called azimuthally polarized annular illumination can be set, insteadof the diffractive optical element 5 for annular illumination, in theillumination optical path, so as to implement the modified illuminationin which the beam passing through the secondary light source of theannular shape is set in the azimuthal polarization state, i.e., theazimuthally polarized annular illumination. FIG. 11 is an illustrationschematically showing the configuration of the diffractive opticalelement for azimuthally polarized annular illumination according to thepresent embodiment. FIG. 12 is an illustration schematically showing thesecondary light source of the annular shape set in the azimuthalpolarization state.

With reference to FIGS. 11 and 12, the diffractive optical element 50for azimuthally polarized annular illumination according to the presentembodiment is constructed in such an arrangement that four types ofbasic elements 50A-50D having the same cross section of a rectangularshape and having their respective thicknesses different from each otheralong the direction of transmission of light (Y-direction) (i.e.,lengths in the direction of the optical axis) are arranged lengthwiseand breadthwise and densely. The thicknesses are set as follows: thethickness of the first basic elements 50A is the largest, the thicknessof the fourth basic elements 50D the smallest, and the thickness of thesecond basic elements 50B is greater than the thickness of the thirdbasic elements 50C.

The diffractive optical element 50 includes an approximately equalnumber of first basic elements 50A, second basic elements 50B, thirdbasic elements 50C, and fourth basic elements 50D, and the four types ofbasic elements 50A-50D are arranged substantially at random.Furthermore, a diffracting surface (indicated by hatching in thedrawing) is formed on the mask side of each basic element 50A-50D, andthe diffracting surfaces of the respective basic elements 50A-50D arearrayed along one plane perpendicular to the optical axis AX (not shownin FIG. 11). As a result, the mask-side surface of the diffractiveoptical element 50 is planar, while the light-source-side surface of thediffractive optical element 50 is uneven due to the differences amongthe thicknesses of the respective basic elements 50A-SOD.

The diffracting surface of each first basic element 50A is arranged toform a pair of arc regions (bow shape) 31A symmetric with respect to anaxis line of the Z-direction passing the optical axis AX, in thesecondary light source 31 of the annular shape shown in FIG. 12. Namely,as shown in FIG. 13, each first basic element 50A has a function offorming a pair of arc (bow shape) light intensity distributions 32Asymmetric with respect to the axis line of the Z-direction passing theoptical axis AX (corresponding to a pair of arc regions 31A) in the farfield 50E of the diffractive optical element 50 (i.e., in the far fieldof each basic element 50A-50D).

The diffracting surface of each second basic element 50B is arranged soas to form a pair of arc (bow shape) regions 31B symmetric with respectto an axis line obtained by rotating the axis line of the Z-directionpassing the optical axis AX, by −45° around the Y-axis (or obtained byrotating it by 45° counterclockwise in FIG. 12). Namely, as shown inFIG. 14, each second basic element SOB has a function of forming a pairof arc (bow shape) light intensity distributions 32B symmetric withrespect to the axis line resulting from the −45° rotation around theY-axis, of the axis line of the Z-direction passing the optical axis AX(corresponding to a pair of arc regions 31B), in the far field 50E.

The diffracting surface of each third basic element 50C is arranged toform a pair of arc (bow shape) regions 31C symmetric with respect to anaxis line of the X-direction passing the optical axis AX. Namely, asshown in FIG. 15, each third basic element 50C has a function of forminga pair of arc (bow shape) light intensity distributions 32C symmetricwith respect to the axis line of the X-direction passing the opticalaxis AX (corresponding to a pair of arc regions 31C), in the far field50E.

The diffracting surface of each fourth basic element 50D is arranged soas to form a pair of arc (bow shape) regions 31D symmetric with respectto an axis line obtained by rotating the axis of the Z-direction passingthe optical axis AX by +45° around the Y-axis (i.e., obtained byrotating it by 45° clockwise in FIG. 12). Namely, as shown in FIG. 16,each fourth basic element 50D has a function of forming a pair of arc(bow shape) light intensity distributions 32D symmetric with respect tothe axis line resulting from the +45° rotation around the Y-axis, of theaxis line of the Z-direction passing the optical axis AX (correspondingto a pair of arc regions 31D), in the far field 50E. The sizes of therespective arc regions 31A-31D are approximately equal to each other,and they form the secondary light source 31 of the annular shapecentered around the optical axis AX, while the eight arc regions 31A-31Dare not overlapping with each other and not spaced from each other.

In the present embodiment, each basic element 50A-50D is made ofcrystalline quartz being an optical material with optical activity, andthe crystallographic axis of each basic element 50A-50D is setapproximately to coincide with the optical axis AX. The optical activityof crystalline quartz will be briefly described below with reference toFIG. 17. With reference to FIG. 17, an optical member 35 of aplane-parallel plate shape made of crystalline quartz and in a thicknessd is arranged so that its crystallographic axis coincides with theoptical axis AX. In this case, by virtue of the optical activity of theoptical member 35, incident, linearly polarized light emerges in a statein which its-polarization direction is rotated by θ around the opticalaxis AX.

At this time, the angle θ of rotation of the polarization direction dueto the optical activity of the optical member 35 is represented by Eq(1) below, using the thickness d of the optical member 35 and therotatory power ρ of crystalline quartz.

θ=d·ρ  (1)

In general, the rotatory power ρ of crystalline quartz tends to increasewith decrease in the wavelength of used light and, according to thedescription on page 167 in “Applied Optics II,” the rotatory power ρ ofcrystalline quartz for light having the wavelength of 250.3 nm is153.9°/mm.

In the present embodiment the first basic elements 50A are designed insuch a thickness dA that when light of linear polarization having thedirection of polarization along the Z-direction is incident thereto,they output light of linear polarization having the polarizationdirection along a direction resulting from +180° rotation of theZ-direction around the Y-axis, i.e., along the Z-direction, as shown inFIG. 13. As a result, the polarization direction of beams passingthrough a pair of arc light intensity distributions 32A formed in thefar field 50E is also the Z-direction, and the polarization direction ofbeams passing through a pair of arc regions 31A shown in FIG. 12 is alsothe Z-direction.

The second basic elements 50B are designed in such a thickness dB thatwhen light of linear polarization having the polarization directionalong the Z-direction is incident thereto, they output light of linearpolarization having the polarization direction along a directionresulting from +135° rotation of the Z-direction around the Y-axis,i.e., along a direction resulting from −45° rotation of the Z-directionaround the Y-axis, as shown in FIG. 14. As a result, the polarizationdirection of beams passing through a pair of arc light intensitydistributions 32B formed in the far field 50E is also the directionobtained by rotating the Z-direction by −45° around the Y-axis, and thepolarization direction of beams passing through a pair of arc regions31A shown in FIG. 12 is also the direction obtained by rotating theZ-direction by −45° around the Y-axis.

The third basic elements 50C are designed in such a thickness dC thatwhen light of linear polarization having the polarization directionalong the Z-direction is incident thereto, they output light of linearpolarization having the polarization direction along a directionresulting from +90° rotation of the Z-direction around the Y-axis, i.e.,along the X-direction, as shown in FIG. 15. As a result, thepolarization direction of beams passing through a pair of arc lightintensity distributions 32C formed in the far field 50E is also theX-direction, and the polarization direction of beams passing through apair of arc regions 31C shown in FIG. 12 is also the X-direction.

The fourth basic elements 50D are designed in such a thickness dD thatwhen light of linear polarization having the polarization directionalong the Z-direction is incident thereto, they output light of linearpolarization having the polarization direction along a directionresulting from +45° rotation of the Z-direction around the Y-axis, asshown in FIG. 16. As a result, the polarization direction of beamspassing through a pair of arc light intensity distributions 32D formedin the far field 50E is also the direction obtained by rotating theZ-direction by +45° around the Y-axis, and the polarization direction ofbeams passing through a pair of arc regions 31D shown in FIG. 12 is alsothe direction obtained by rotating the Z-direction by +45° around theY-axis.

In the present embodiment, the diffractive optical element 50 forazimuthally polarized annular illumination is set in the illuminationoptical system on the occasion of effecting the azimuthally polarizedannular illumination, whereby the light of linear polarization havingthe polarization direction along the Z-direction is made incident to thediffractive optical element 50. As a result, the secondary light sourceof the annular shape (illumination pupil distribution of annular shape)31 is formed on the rear focal plane of the micro fly's eye lens 12(i.e., on or near the illumination pupil), as shown in FIG. 12, and thebeams passing through the secondary light source 31 of the annular shapeare set in the azimuthal polarization state.

In the azimuthal polarization state, the beams passing through therespective arc regions 31A-31D constituting the secondary light source31 of the annular shape turn into the linearly polarized state havingthe polarization direction substantially coincident with a tangent lineto a circle centered around the optical axis AX, at the central positionalong the circumferential direction of each arc region 31A-31D.

In the present embodiment, as described above, the beam transformingelement 50 for forming the predetermined light intensity distribution onthe predetermined surface on the basis of the incident beam comprisesthe first basic element 50A made of the optical material with opticalactivity, for forming the first region distribution 32A of thepredetermined light intensity distribution on the basis of the incidentbeam; and the second basic element 50B made of the optical material withoptical activity, for forming the second region distribution 32B of thepredetermined light intensity distribution on the basis of the incidentbeam, and the first basic element 50A and the second basic element 50Bhave their respective thicknesses different from each other along thedirection of transmission of light.

Thanks to this configuration, the present embodiment is able to form thesecondary light source 31 of the annular shape in the azimuthalpolarization state, with no substantial loss of light quantity, throughthe diffracting action and optical rotating action of the diffractiveoptical element 50 as the beam transforming element, different from theconventional technology giving rise to the large loss of light quantityat the aperture stop.

In a preferred form of the present embodiment, the thickness of thefirst basic element 50A and the thickness of the second basic element50B are so set that with incidence of linearly polarized light thepolarization direction of the linearly polarized light forming the firstregion distribution 32A is different from the polarization direction ofthe linearly polarized light forming the second region distribution 32B.Preferably, the first region distribution 32A and the second regiondistribution 32B are positioned in at least a part of a predeterminedannular region, which is a predetermined annular region centered arounda predetermined point on the predetermined surface, and the beamspassing through the first region distribution 32A and through the secondregion distribution 32B have a polarization state in which a principalcomponent is linearly polarized light having the polarization directionalong the circumferential direction of the predetermined annular region.

In this case, preferably, the predetermined light intensity distributionhas a contour of virtually the same shape as the predetermined annularregion, the polarization state of the beam passing through the firstregion distribution 32A has a linear polarization componentsubstantially coincident with a tangential direction to a circlecentered around a predetermined point at the central position along thecircumferential direction of the first region distribution 32A, and thepolarization state of the beam passing through the second regiondistribution 32B has a linear polarization component substantiallycoincident with a tangential direction to a circle centered around apredetermined point at the central position along the circumferentialdirection of the second region distribution 32B. In another preferredconfiguration, the predetermined light intensity distribution is adistribution of a multipole shape in the predetermined annular region,the polarization state of the beam passing through the first regiondistribution has a linear polarization component substantiallycoincident with a tangential direction to a circle centered around apredetermined point at the central position along the circumferentialdirection of the first region distribution, and the polarization stateof the beam passing through the second region distribution has a linearpolarization component substantially coincident with a tangentialdirection to a circle centered around a predetermined point at thecentral position along the circumferential direction of the secondregion distribution.

In a preferred form of the present embodiment, the first basic elementand the second basic element are made of an optical material with anoptical rotatory power of not less than 100°/mm for light of awavelength used. Preferably, the first basic element and the secondbasic element are made of crystalline quartz. The beam transformingelement preferably includes virtually the same number of first basicelements and second basic elements. The first basic element and thesecond basic element preferably have diffracting action or refractingaction.

In another preferred form of the present embodiment, preferably, thefirst basic element forms at least two first region distributions on thepredetermined surface on the basis of the incident beam, and the secondbasic element forms at least two second region distributions on thepredetermined surface on the basis of the incident beam. In addition,preferably, the beam transforming element further comprises the thirdbasic element 50C made of the optical material with optical activity,for forming the third region distribution 32C of the predetermined lightintensity distribution on the basis of the incident beam, and the fourthbasic element SOD made of the optical material with optical activity,for forming the fourth region distribution 32D of the predeterminedlight intensity distribution on the basis of the incident beam.

In the present embodiment, the beam transforming element 50 for formingthe predetermined light intensity distribution of the shape differentfrom the sectional shape of the incident beam, on the predeterminedsurface, has the diffracting surface or refracting surface for formingthe predetermined light intensity distribution on the predeterminedsurface, the predetermined light intensity distribution is adistribution in at least a part of a predetermined annular region, whichis a predetermined annular region centered around a predetermined pointon the predetermined surface, and the beam from the beam transformingelement passing through the predetermined annular region has apolarization state in which a principal component is linearly polarizedlight having the direction of polarization along the circumferentialdirection of the predetermined annular region.

In the configuration as described above, the present embodiment,different from the conventional technology giving rise to the large lossof light quantity at the aperture stop, is able to form the secondarylight source 31 of the annular shape in the azimuthal polarizationstate, with no substantial loss of light quantity, through thediffracting action and optical rotating action of the diffractiveoptical element 50 as the beam transforming element.

In a preferred form of the present embodiment, the predetermined lightintensity distribution has a contour of a multipole shape or annularshape. The beam transforming element is preferably made of an opticalmaterial with optical activity.

The illumination optical apparatus of the present embodiment is theillumination optical apparatus for illuminating the surface to beilluminated, based on the beam from the light source, and comprises theabove-described beam transforming element for transforming the beam fromthe light source in order to form the illumination pupil distribution onor near the illumination pupil of the illumination optical apparatus. Inthis configuration, the illumination optical apparatus of the presentembodiment is able to form the illumination pupil distribution of theannular shape in the azimuthal polarization state while well suppressingthe loss of light quantity.

Here the beam transforming element is preferably arranged to bereplaceable with another beam transforming element having a differentcharacteristic. Preferably, the apparatus further comprises thewavefront splitting optical integrator disposed in the optical pathbetween the beam transforming element and the surface to be illuminated,and the beam transforming element forms the predetermined lightintensity distribution on the entrance surface of the optical integratoron the basis of the incident beam.

In a preferred form of the illumination optical apparatus of the presentembodiment, at least one of the light intensity distribution on thepredetermined surface and the polarization state of the beam from thebeam transforming element passing through the predetermined annularregion is set in consideration of the influence of an optical memberdisposed in the optical path between the light source and the surface tobe illuminated. Preferably, the polarization state of the beam from thebeam transforming element is so set that the light illuminating thesurface to be illuminated is in a polarization state in which aprincipal component is S-polarized light.

The exposure apparatus of the present embodiment comprises theabove-described illumination optical apparatus for illuminating themask, and projects the pattern of the mask onto the photosensitivesubstrate. Preferably, at least one of the light intensity distributionon the predetermined surface and the polarization state of the beam fromthe beam transforming element passing through the predetermined annularregion is set in consideration of the influence of an optical memberdisposed in the optical path between the light source and thephotosensitive substrate. Preferably, the polarization state of the beamfrom the beam transforming element is so set that the light illuminatingthe photosensitive substrate is in a polarization state in which aprincipal component is S-polarized light.

The exposure method of the present embodiment comprises the illuminationstep of illuminating the mask by use of the above-described illuminationoptical apparatus, and the exposure step of projecting the pattern ofthe mask onto the photosensitive substrate. Preferably, at least one ofthe light intensity distribution on the predetermined surface and thepolarization state of the beam from the beam transforming elementpassing through the predetermined annular region is set in considerationof the influence of an optical member disposed in the optical pathbetween the light source and the photosensitive substrate. Preferably,the polarization state of the beam from the beam transforming element isso set that the light illuminating the photosensitive substrate is in apolarization state in which a principal component is S-polarized light.

In other words, the illumination optical apparatus of the presentembodiment is able to form the illumination pupil distribution of theannular shape in the azimuthal polarization state while well suppressingthe loss of light quantity. As a result, the exposure apparatus of thepresent embodiment is able to transcribe the microscopic pattern in anarbitrary direction under an appropriate illumination conditionfaithfully and with high throughput because it uses the illuminationoptical apparatus capable of forming the illumination pupil distributionof the annular shape in the azimuthal polarization state while wellsuppressing the loss of light quantity.

In the azimuthally polarized annular illumination based on theillumination pupil distribution of the annular shape in the azimuthalpolarization state, the light illuminating the wafer W as a surface tobe illuminated is in the polarization state in which the principalcomponent is the S-polarized light. Here the S-polarized light islinearly polarized light having the direction of polarization along adirection normal to a plane of incidence (i.e., polarized light with theelectric vector oscillating in the direction normal to the plane ofincidence). The plane of incidence herein is defined as the followingplane: when light arrives at a boundary surface of a medium (a surfaceto be illuminated: surface of wafer W), the plane includes the normal tothe boundary plane at the arrival point and the direction of incidenceof light.

In the above-described embodiment, the diffractive optical element 50for azimuthally polarized annular illumination is constructed byrandomly arranging virtually the same number of four types of basicelements 50A-50D with the same rectangular cross section lengthwise andbreadthwise and densely. However, without having to be limited to this,a variety of modification examples can be contemplated as to the numberof basic elements of each type, the sectional shape, the number oftypes, the arrangement, and so on.

In the above-described embodiment, the secondary light source 31 of theannular shape centered around the optical axis AX is composed of theeight arc regions 31A-31D arrayed without overlapping with each otherand without being spaced from each other, using the diffractive opticalelement 50 consisting of the four types of basic elements 50A-50D.However, without having to be limited to this, a variety of modificationexamples can be contemplated as to the number of regions forming thesecondary light source of the annular shape, the shape, the arrangement,and so on.

Specifically, as shown in FIG. 18A, it is also possible to form asecondary light source 33 a of an octapole shape in the azimuthalpolarization state consisting of eight arc (bow shape) regions spacedfrom each other along the circumferential direction, for example, usingthe diffractive optical element consisting of four types of basicelements. In addition, as shown in FIG. 18B, it is also possible to forma secondary light source 33 b of a quadrupole shape in the azimuthalpolarization state consisting of four arc (bow shape) regions spacedfrom each other along the circumferential direction, for example, usingthe diffractive optical element consisting of four types of basicelements. In the secondary light source of the octapole shape or thesecondary light source of the quadrupole shape, the shape of each regionis not limited to the arc shape, but it may be, for example, circular,elliptical, or sectorial. Furthermore, as shown in FIG. 19, it is alsopossible to form a secondary light source 33 c of an annular shape inthe azimuthal polarization state consisting of eight arc regionsoverlapping with each other along the circumferential direction, forexample, using the diffractive optical element consisting of four typesof basic elements.

In addition to the quadrupole or octapole secondary light source in theazimuthal polarization state consisting of the four or eight regionsspaced from each other along the circumferential direction, thesecondary light source may be formed in a hexapole shape in theazimuthal polarization state and of six regions spaced from each otheralong the circumferential direction, as shown in FIG. 20A. In addition,as shown in FIG. 20B, the secondary light source may be formed as onehaving secondary light source of a multipole shape in the azimuthalpolarization state consisting of a plurality of regions spaced from eachother along the circumferential direction, and a secondary light sourceon the center pole in the unpolarized state or linearly polarized stateconsisting of a region on the optical axis. Furthermore, the secondarylight source may also be formed in a dipole shape in the azimuthalpolarization state and of two regions spaced from each other along thecircumferential direction.

In the aforementioned embodiment, as shown in FIG. 11, the four types ofbasic elements 50A-50D are individually formed, and the diffractiveoptical element 50 is constructed by combining these elements. However,without having to be limited to this, the diffractive optical element 50can also be integrally constructed in such a manner that a crystallinequartz substrate is subjected, for example, to etching to form theexit-side diffracting surfaces and the entrance-side uneven surfaces ofthe respective basic elements 50A-50D.

In the aforementioned embodiment each basic element 50A-50D (therefore,the diffractive optical element 50) is made of crystalline quartz.However, without having to be limited to this, each basic element canalso be made of another appropriate optical material with opticalactivity. In this case, it is preferable to use an optical material withan optical rotatory power of not less than 100°/mm for light of awavelength used. Specifically, use of an optical material with a lowrotatory power is undesirable because the thickness necessary forachieving the required rotation angle of the polarization directionbecomes too large, so as to cause the loss of light quantity.

The aforementioned embodiment is arranged to form the illumination pupildistribution of the annular shape (secondary light source), but, withouthaving to be limited to this, the illumination pupil distribution of acircular shape can also be formed on or near the illumination pupil. Inaddition to the illumination pupil distribution of the annular shape andthe illumination pupil distribution of the multipole shape, it is alsopossible to implement a so-called annular illumination with the centerpole and a multipole illumination with the center pole, for example, byforming a center region distribution including the optical axis.

In the aforementioned embodiment, the illumination pupil distribution inthe azimuthal polarization state is formed on or near the illuminationpupil. However, the polarization direction can vary because ofpolarization aberration (retardation) of an optical system (theillumination optical system or the projection optical system) closer tothe wafer than the diffractive optical element as the beam transformingelement. In this case, it is necessary to properly set the polarizationstate of the beam passing through the illumination pupil distributionformed on or near the illumination pupil, with consideration to theinfluence of polarization aberration of these optical systems.

In connection with the foregoing polarization aberration, reflectedlight can have a phase difference in each polarization direction becauseof a polarization characteristic of a reflecting member disposed in theoptical system (the illumination optical system or the projectionoptical system) closer to the wafer than the beam transforming element.In this case, it is also necessary to properly set the polarizationstate of the beam passing through the illumination pupil distributionformed on or near the illumination pupil, with consideration to theinfluence of the phase difference due to the polarization characteristicof the reflecting member.

The reflectance in the reflecting member can vary depending upon thepolarization direction, because of a polarization characteristic of areflecting member disposed in the optical system (the illuminationoptical system or the projection optical system) closer to the waferthan the beam transforming element. In this case, it is desirable toprovide offsets on the light intensity distribution formed on or nearthe illumination pupil, i.e. to provide a distribution of numbers ofrespective basic elements, in consideration of the reflectance in eachpolarization direction. The same technique can also be similarly appliedto cases where the transmittance in the optical system closer to thewafer than the beam transforming element varies depending upon thepolarization direction.

In the foregoing embodiment, the light-source-side surface of thediffractive optical element 50 is of the uneven shape with leveldifferences according to the differences among the thicknesses ofrespective basic elements 50A-50D. Then the surface on the light sourceside (entrance side) of the diffractive optical element 50 can also beformed in a planar shape, as shown in FIG. 21, by adding a compensationmember 36 on the entrance side of the basic elements except for thefirst basic elements 50A with the largest thickness, i.e., on theentrance side of the second basic elements 50B, third basic elements50C, and fourth basic elements 50D. In this case, the compensationmember 36 is made of an optical material without optical activity.

The aforementioned embodiment shows the example wherein the beam passingthrough the illumination pupil distribution formed on or near theillumination pupil has only the linear polarization component along thecircumferential direction. However, without having to be limited tothis, the expected effect of the present invention can be achieved aslong as the polarization state of the beam passing through theillumination pupil distribution is a state in which the principalcomponent is linearly polarized light having the polarization directionalong the circumferential direction.

The foregoing embodiment uses the diffractive optical element consistingof the plural types of basic elements having the diffracting action, asthe beam transforming element for forming the light intensitydistribution of the shape different from the sectional shape of theincident beam, on the predetermined plane, based on the incident beam.However, without having to be limited to this, it is also possible touse as the beam transforming element a refracting optical element, forexample, consisting of plural types of basic elements having refractingsurfaces virtually optically equivalent to the diffracting surfaces ofthe respective basic elements, i.e., consisting of plural types of basicelements having the refracting action.

The exposure apparatus according to the foregoing embodiment is able toproduce microdevices (semiconductor elements, image pickup elements,liquid crystal display elements, thin-film magnetic heads, etc.) byilluminating a mask (reticle) by the illumination optical apparatus(illumination step) and projecting a pattern for transcription formed onthe mask, onto a photosensitive substrate by use of the projectionoptical system (exposure step). The following will describe an exampleof a procedure of producing semiconductor devices as microdevices byforming a predetermined circuit pattern on a wafer or the like as aphotosensitive substrate by means of the exposure apparatus of theforegoing embodiment, with reference to the flowchart of FIG. 22.

The first step 301 in FIG. 22 is to deposit a metal film on each, ofwafers in one lot. The next step 302 is to apply a photoresist onto themetal film on each wafer in the lot. Thereafter, step 303 is tosequentially transcribe an image of a pattern on a mask into each shotarea on each wafer in the lot, through the projection optical system byuse of the exposure apparatus of the foregoing embodiment. Subsequently,step 304 is to perform development of the photoresist on each wafer inthe lot, and step 305 thereafter is to perform etching with the resistpattern as a mask on each wafer in the lot, thereby forming a circuitpattern corresponding to the pattern on the mask, in each shot area oneach wafer. Thereafter, devices such as semiconductor elements areproduced through execution of formation of circuit patterns in upperlayers and others. The semiconductor device production method asdescribed above permits us to produce the semiconductor devices withextremely fine circuit patterns at high throughput.

The exposure apparatus of the foregoing embodiment can also be appliedto production of a liquid crystal display element as a microdevice insuch a manner that predetermined patterns (a circuit pattern, anelectrode pattern, etc.) are formed on a plate (glass substrate). Anexample of a procedure of this production will be described below withreference to the flowchart of FIG. 23. In FIG. 23, pattern forming step401 is to execute a so-called photolithography step of transcribing apattern on a mask onto a photosensitive substrate (a glass substratecoated with a resist or the like) by use of the exposure apparatus ofthe foregoing embodiment. In this photolithography step, thepredetermined patterns including a number of electrodes and others areformed on the photosensitive substrate. Thereafter, the exposedsubstrate is subjected to steps such as a development step, an etchingstep, a resist removing step, etc., to form the predetermined patternson the substrate, followed by next color filter forming step 402.

The next color filter forming step 402 is to form a color filter inwhich a number of sets of three dots corresponding to R (Red), G(Green), and B (Blue) are arrayed in a matrix, or in which a pluralityof sets of filters of three stripes of R, G and B are arrayed in thedirection of horizontal scan lines. After the color filter forming step402, cell assembly step 403 is carried out. The cell assembly step 403is to assemble a liquid crystal panel (liquid crystal cell), using thesubstrate with the predetermined patterns obtained in the patternforming step 401, the color filter obtained in the color filter formingstep 402, and so on.

In the cell assembly step 403, for example, a liquid crystal is pouredinto the space between the substrate with the predetermined patternsobtained in the pattern forming step 401 and the color filter obtainedin the color filter forming step 402 to produce the liquid crystal panel(liquid crystal cell). Thereafter, module assembly step 404 is carriedout to attach such components as an electric circuit, a backlight, andso on for implementing the display operation of the assembled liquidcrystal panel (liquid crystal cell), to complete the liquid crystaldisplay element. The production method of the liquid crystal displayelement described above permits us to produce the liquid crystal displayelements with extremely fine circuit patterns at high throughput.

The foregoing embodiment is arranged to use the KrF excimer laser light(wavelength: 248 nm) or the ArF excimer laser light (wavelength: 193 nm)as the exposure light, but, without having to be limited to this, thepresent invention can also be applied to other appropriate laser lightsources, e.g., an F₂ laser light source for supplying laser light of thewavelength of 157 nm. Furthermore, the foregoing embodiment describedthe present invention, using the exposure apparatus with theillumination optical apparatus as an example, but it is apparent thatthe present invention can be applied to ordinary illumination opticalapparatus for illuminating the surface to be illuminated, except for themask and wafer.

In the foregoing embodiment, it is also possible to apply the so-calledliquid immersion method, which is a technique of filling a medium(typically, a liquid) with a refractive index larger than 1.1 in theoptical path between the projection optical system and thephotosensitive substrate. In this case, the technique of filling theliquid in the optical path between the projection optical system and thephotosensitive substrate can be selected from the technique of locallyfilling the liquid as disclosed in PCT International Publication No.WO99/49504, the technique of moving a stage holding a substrate as anexposure target in a liquid bath as disclosed in Japanese PatentApplication Laid-Open No. 6-124873, the technique of forming a liquidbath in a predetermined depth on a stage and holding the substratetherein as disclosed in Japanese Patent Application Laid-Open No.10-303114, and so on. The PCT International Publication No. WO99/49504,Japanese Patent Application Laid-Open No. 6-124873, and Japanese PatentApplication Laid-Open No. 10-303114 are incorporated herein byreference.

The liquid is preferably one that is transparent to the exposure light,that has the refractive index as high as possible, and that is stableagainst the projection optical system and the photoresist applied to thesurface of the substrate; for example, where the exposure light is theKrF excimer laser light or the ArF excimer laser light, pure water ordeionized water can be used as the liquid. Where the F₂ laser light isused as the exposure light, the liquid can be a fluorinated liquidcapable of transmitting the F₂ laser light, e.g., fluorinated oil orperfluoropolyether (PFPE).

From the invention thus described, it will be obvious that the inventionmay be varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedfor inclusion within the scope of the following claims.

What is claimed is:
 1. An illumination optical apparatus forilluminating a pattern on a mask with illumination light, comprising: anillumination optical system including a polarization optical member madeof optical material with optical rotatory power, configured toilluminate the pattern with the illumination light which enters into thepolarization optical member and has a polarization state of asubstantially single linearly polarization component as a principlecomponent, in a polarization state in which a principle component is Spolarized light, through a pupil plane of the illumination opticalsystem, wherein a first thickness of the polarization optical member inan optical path of a first illumination light which passes through afirst position of the pupil plane is different from a second thicknessof the polarization optical member in an optical path of a secondillumination light which passes through a second position of the pupilplane.